The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.
The present invention relates generally to slab laser materials and more specifically to a laser design that uses two similar materials, one laser active and one not active, that are bonded together to form a composite slab of material. Appropriate antireflection coatings (to pump through) or TIR preserving and bonding coatings (to heatsink to) are placed on the TIR surfaces of the slab.
Slab laser materials and disk lasers share some aspects of the invention. These laser geometries have been described by multiple groups, and examples are described in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,725,787
U.S. Pat. No. 6,134,258
U.S. Pat. No. 6,094,297
U.S. Pat. No. 5,651,021
The best reference is the Phase-conjugated hybrid slab laser of U.S. Pat. No. 4,725,787. It shows a relatively low-power but high-quality laser oscillator couple to a high-power laser amplifier. The amplifier includes a rectangular slab of laser active material, and a phase-conjugate end mirror.
The present invention is a laser design that provides a method to efficiently pump laser materials so that pump energy is confined to the amplifying mode volume. Especially useful in quasi-three level materials because the design reduces the effect of reabsorption in weakly pumped regions of the gain media. Provides a higher damage threshold than that achieved in thin disk laser media.
As mentioned above, slab laser materials and disk lasers share some aspects of the invention. These laser geometries have been described by multiple groups.
One embodiment uses a slab of active laser material, for instance Yb:YAG, capped by a nonactive material, for instance undoped YAG or sapphire. The two materials are bonded together, for instance by diffusion bonding. The composite slab is then cut and polished to serve as a laser gain module. The slab can be Brewster-cut or flat-flat and antireflection coated on the ends. Alternatively, the nonactive material can be sandwiched between two active regions.
The slab is pumped from the top face like a disk laser or from the end like a longitudinally pumped slab. The slab could also be side-pumped using close coupled diodes. The preferred pumping mechanism depends on the pump source used. The slab generates or amplifies a laser beam that is longitudinally coupled into the device through the end (possibly Brewster-cut) surfaces. The laser beam bounces via total internal reflection within the slab passing one or more times through the active part(s) of the medium. The active region can vary in thickness. The thickness is chosen to minimize thermal and/or stress gradients in the material.
One of both of the large flat TIR surfaces of the slab is placed against a heatsink. A multilayer coating consisting of (1) a TIR preserving coating and a metallic coating is placed on each of the TIR-surfaces. In some embodiments a highly reflecting dielectric coating is also placed between the TIR preserving and metallic coating. The other TIR surface can be antireflection coated, for instance to pump through, or have the TIR preserving and metallic coatings to serve as a cooling surface.
All embodiment of the invention use two similar materials, one laser active and one not active, that are bonded together to form a composite slab of material. Appropriate antireflection coatings (to pump through) or TIR preserving and bonding coatings (to heatsink to) are placed on the TIR surfaces of the slab.